implementation of automatic lift axle system for trucks with … · liftable axle mechanism types...

*Corresponding author: Address: Ford Otosan R&D Center, Akpınar Mh. Hasan Basri Cd. No: 2, 34885 Sancaktepe

İstanbul TURKEY e-mail address: [email protected], Phone: +90 216 664 3478

Implementation of Automatic Lift Axle System for Trucks with Mechanical

Suspension

*1,2

Taylan Keleş, 2Ahmet Aray,

2Ufuk Özdemir,

1Erdinç Altuğ,

3Levent Güvenç

1İstanbul Technical University, Faculty of Mechanical Engineering, İstanbul, Turkey

2Ford Otosan R&D Center, Sancaktepe, İstanbul, Turkey

3Department of Mechanical and Aerospace Engineering, Ohio State University

201 W 19th Ave E303, Columbus, OH 43210, USA

Abstract The aim of an automatic lift axle auto-drop system is to drop the appropriate liftable axle of a truck

automatically based on the loading condition, instead of being manually controlled by the driver. In

this paper, addition to previous studies, experimental implementation of an AutoDrop system to a truck

suspended with compensating arm type mechanical suspension is told. Weight estimation for

compensating arm type suspension has challenge because of articulation working and huge hysteresis

characteristic. An approach is brought and analyzed for weight estimation for the axles with

compensating arm using height sensors resulting higher accuracy. An improved algorithm is developed

and lift axle system becomes automatized to satisfy the rules mentioned in EU Directive 1230/2012

EEC. An algorithm is achieved by Coding and implementing the software using Electronic Control

Unit mounted in Cab.

Key words: Autodrop, Axle Load, Compensating Arm, Mechanical Suspension

1. Introduction

In Turkey and all over the world, highways share most of the transportation load. Highways are

expensive investments that must be protected. Commercial vehicles transporting heavy load are

an important contributor to the deterioration of the pavement of a highway. Overloading these

vehicles leads to the application of excessive pressure per unit area of the road and eventual

pavement damage. In order to restore the damage caused by overweight trucks, huge capital

investments are needed to upgrade and rehabilitate the existing road network to make it capable

to withstand high stresses and tyre pressures caused by heavy wheel loads [1]. There have been

many studies performed questioning increased axle load effect on pavement performance, service

life and maintenance costs. According to study performed by H.M.A. Salem [2], the maximum

allowable axle load should not exceed 11 tons during summer season and should not exceed 14

tons during winter, yet more single axle loads greater than 14 tons should not be allowed even

with penalties because it will cause a quick deterioration to the pavement, especially during

summer. Additionally, by allowing the axle loads to be increased from 10 to 13 tones, the

pavements will last to only one half of its design life compared to the 10 tons axle while study

performed by S. Hatipoğlu [3] in Turkey indicates that lowering the legal weight limit than can

be supported by a single axle from 13 tons to 11.5 tons results in a corresponding increase in the

durability of the highway by up to 32%. One of the factors for overloaded axle is liftable axles by

T. KELES et al./ ISITES2015 Valencia -Spain 805

transferring axle load to the other axles when lifted position for laden trucks.

The main purpose of the axle-lift device is to raise the axle in order to reduce fuel consumption,

tire wear and easier take off on slippery surfaces while the vehicle is not fully loaded. In 2016,

the lift axle dropping system is expected to be a legal obligation for heavy commercial trucks in

Turkey. The aim of an automatic lift axle auto-drop system is to drop the appropriate axle(s)

automatically based on the loading condition, instead of being manually controlled by the driver.

According to EU Directive 1230/2012 EEC Mass and Dimensions Policy, the manufacturer must

ensure that under all driving conditions, the mass corresponding to each axle or axle groups must

be within permissible limits except when taking off the slippery surfaces. There are a couple of

systems that satisfy all the obligatory rules on air suspension mounted axles however there is not

a feasible system implemented on mechanically suspended trucks with tag axle around the world.

In Europe where 1230/2012 EEC is already legislated, all retractable axle fitted vehicles are

equipped with air suspension systems. However in Turkey, heavy commercial trucks that have

mechanical suspension systems are quite popular. Therefore, the aim of the project is to construct

a control mechanism that senses the axle loads and lowers the retractable axle automatically if the

nearest axle or axle groups exceed the limits for mechanically suspended trucks with

compensating arm type suspension in order to prevent pavement performance of the road to be

reduced.

This paper provides an overview of both algorithm and associated simulator developed for heavy

commercial truck with mechanical suspension. During the simulations, the condition of the

truck’s load is used as an input and the automatic lift axle system algorithm decides on the axle(s)

that should be dropped. In order to complete a full algorithm, inputs and state-flow chart should

be determined. In Section 2 the structure of lift axle mechanisms and boundary diagram for an

automatic lift axle system will be introduced. It will be seen that all inputs but axle loads can be

derived from vehicle communication line, CAN Bus with J1939 protocol. The algorithm is

designed for requirements declared in EU Directive 1230/2012 EEC Masses and Dimensions

Policy.

In Section 3 with the advantage of performing co-simulation, the algorithm coded using

SIMULINK/Matlab is validated using TruckMaker Virtual Truck Simulation Program by

defining a generic truck which is having 8x2S axle configuration with 2 liftable axles and

assumption of deriving axle loads from virtual truck model. In Section 4, an approach is brought

and analyzed for weight estimation for the axles with compensating arm type suspension using

height sensors resulting higher accuracy. In Section 5 by completing the calculation all the inputs

including axle loads, the system is implemented a Ford Cargo 3238S truck using PI INNOVO

openECU m250 electronic control unit. Proposed algorithm and axle load estimation

performances are tested on the vehicle and results are examined.

2. Automatic Lift Axle System

8x2S vehicle is analyzed as it is the worst case in terms of axle configuration. There are two

liftable axles indicated in Figure 1. Those axles have different lifting mechanisms but both are

controlled same.


Figure 1. Mechanically suspended truck has 8x2S axle configuration with 2 liftable axles.

Lift axle system comprises of the air compressor, air bags, valves and some mechanical coupling

elements. The air compressor provides pressured air to air bags in order to push or pull the axle to

position it in either its lifted or lowered condition. Valves control the air flow between the air

bags and the air compressor and are also used for exhausting the air from the air bag.

Figure 2. Liftable axle mechanism types

In manual usage solenoid valves are controlled by switches mounted in instrumental panel in

cabin. In order to lift/drop the axle, driver pushes corresponding switch and the axle is actuated

directly, regardless of vehicle conditions. However in AutoDrop system, brought by this paper, a

electronic control unit is used in order to actuate solenoid valves. All environmental components,

e.g. switches, lift axle solenoid valves, sensors, are connected to control unit and axles are

actuated by running algorithm designed according to regulatory and truck design in ECU.

2.1. System Requirements and Algorithm

Main requirement for AutoDrop system is obviously calculating axle loads. By definition, system

must drop the appropriate axle(s) automatically based on the loading condition declared in

regulatory as summarized below:

Table 1. Permissible Axle Loads Declared in Masses and Dimensions Policy

Vehicle Condition 1

st Axle 2

nd Axle 3

rd Axle 4

th Axle

All axles are on ground 7.1 ton 25.0 tons (sum of rear axle weight)

2nd

axle is lifted 7.1 ton - 18.0 tons

2nd

and 4th

axles are lifted 7.1 ton - 11.5tons -


By definition e.g. if 2nd

axle is lifted and if rear axle group load exceeds 18.0 tons system will

drop nearest axle which is 2nd

axle in order to share overload and maintain axle loads under

permissible limits and does not allow driver to lift again. Other conditions that do not involve

axle loads are also included in regulation in addition to the conditions given above. For instance,

once ignition is off, all axles should be lowered in order to prevent tires to be stolen. This feature

can be performed by running ECU even if ignition is off. Speed limit is taken into account for

functional requirements to provide safety driving by disabling any driver input after 30 kph.

Additionally in order to improve emergency brake performance when parking brake is engaged

tag axle (4th

axle) should be dropped or not allowed to be lifted by driver since wheels should be

contacted with road surface. An algorithm satisfies all requirement included is designed with the

given I/O table:

Table 2. AutoDrop System Input/Output List

Parameter Signal Description Range

Axle Loads Analogue Load input for each axles.

DR_A2 Digital 2nd

axle lift/drop button input Input

DR_A4 Digital 4th

axle lift/drop button input Input

Ignition Digital Ignition is ON OFF information Input

ECU_A2 Digital 2nd

axle lift/drop actuation signal Output

ECU_A4 Digital 4th

axle lift/drop actuation signal Output

A2_SIG CAN Tx 2nd

axle liftable/not liftable info Output

A4_SIG CAN Tx 4th

axle liftable/not liftable info Output

Hold_PSU Digital Hold Power Supply Unit even if

İgnition is OFF

Output

pbrake CAN Rx Parking Brake information Input

v_speed CAN Rx Vehicle Speed information Input

State-Flow Chart is designed as shown Figure 4. The conditions Q0, Q1 and Q2, represent the

different positions where axles can be placed [4]. There are 3 different conditions where axles

can be placed in a truck with 8x2S axle configuration, two of which are liftable. State transition

conditions are defined according to functional requirements declared in this section. As an

addition to previous study [4], each state has its own sub-routines where detailed axle

information e.g. axle is being lifted, axle cannot be dropped, axle cannot be lifted are stored. For

instance, Q1 indicates that 2nd

axle is lifted and 4th

axle is dropped. Parameter ‘x3’ is the

transition condition in order to lift 4th

axle and defined as below:

Front axle load should be below 7.1 tons

Rear group axle load should be below 11.5 tons

Parking brake should be released

Vehicle speed should be below 30 kph.

Ignition should be ON.


Figure 4. System State-Flow Chart Macro View

3. TruckMaker Simulation

It can be seen from Table 2 that all the inputs but axle loads can be derived directly considering

vehicle implementation. Assuming the axle loads can be derived correctly, firstly, designed

algorithm should be tested. Prototype vehicle simulation model is constructed for this purpose.

TruckMaker as vehicle simulation program is used to model the vehicle, environment, driver

maneuver and driving scenarios. SIMULINK is used to implement the algorithm, driver inputs

and axle movement command to TruckMaker. TruckMaker and SIMULINK can process co-

simulation almost in real-time as simulation speed which is a great advantage because same

algorithm codes written in SIMULINK for TruckMaker can be also used for openECU that

mounted in truck.

Figure 5.TruckMaker and AutoDrop Software Coded in SIMULINK Co-Simulation

Lift/Drop axle is not defined in TruckMaker as a function. Thus to simulate proper axle

movement and axle load distributions, z-axes of tires are altered from software by using discrete

integrator.

Figure 6.Axle movement commands


System input and outputs are re-organized to TruckMaker parameters:

Table 3. AutoDrop System Input/Output List

Parameter Signal Description Data Name

G1 Read Front Axle Load

G2 Read 2nd

Axle Load (Self Steer) Car.SpringFx2.Frc

G3 Read 3rd

Axle Load (Drive Axle) Car.SpringRx.Frc

G4 Read 4th

Axle lift/drop button input Car.SpringRx2.Frc

Brake Write Brake Pedal DM.Brake

Clutch Write Clutch Pedal DM.Clutch

Ignition Read Ignition Information DM.EngineSwitch

Gas Write Gas Pedal DM.Gas

AxlePos Write Axle Lift/Drop z-position Car.CFxx.tz_ext

4. Axle Load Calculation

The basic function of AutoDrop system is to generate appropriate control signal according to axle

loads and positions. Thus axle load must be estimated in order to construct an implementable

system. This can be achieved by measuring the deflection of springs in other words the distance

between axle and chassis arm with using deflection sensors. The set up consisted of an 8x2 self-

steer vehicle as a worst case vehicle type, displacement sensors mounted at different positions on

each axle, an ECU from Pi Innovo used to test algorithm and data collection, weight pads to

understand the corresponding wheel load of the axle as it shown in Figure 7. Mass estimation

models are trained for each individual axle that are front-steering axle and the rear group axle

called tandem axle unit as drive axle and tag axle interconnected with compensating arm type

suspension in order to find correlation between axle load and deflection sensor outputs.

Figure 7.Training Data Collection Tests (Axle Loads and Sensor output)

4.1. Front Axle Suspension Load

Front axle’s leaf springs are single mounted springs and have linear load-deflection correlation

that has less hysteresis difference between loading and unloading states which is approximately

250 kg. In result, front axle mass estimation model can be extracted using conventional methods

with following equation:

bavG front 1 (3.1)


In equation 3.1, 1v refers to deflection sensor output signal attached to corresponding axle. In

order to achieve front axle load frontG , a and b is found as 1429 and 64.08 with experimental

studies by collection training data and curve fitting. Once the coefficients are found, axle load can

be estimated by just using deflection sensor in online-tests.

Figure 8. Front Axle Load Linear Function

4.2. Rear Axle Compensating Arm Type Suspension Load

The mechanical suspension mounted trucks generally have interconnected axles on rear axle

groups to share the load appropriately on rough roads and the geometry should be adequate in

order to balance the load transfer between the axle groups according to the axle capacities. The

tandem axle unit as rear group axle’s mass estimation model is the challenge here because of

drive axle and tag axle that are the elements of tandem axle unit connected each other by a

balancer. So their displacements affected each other and correlation between load and deflection

extracted accordingly.

hgvfvG drive 43 (3.2)

In equation 3.2, 3v and 4v refer to sensor outputs connected to drive axle and tag axle which are

elements of compensating arm type suspension.

Figure 9. New (left) and conventional (right) methods for Axle Load Estimation

For mass estimation model training especially for tandem axle unit many different vehicle


scenarios were tried on each loading condition and nearly 90 different loading conditions in

different sequences were used in test specification. The mass distribution characteristics were

identified from the combination of vehicle and loading cases. The pre-defined mathematical

function parameters are optimized according to collected training data as 4951, 6324 and -28880.

5. Vehicle Implementation

Online axle load calculation is available by entering axle load function parameter to designed

software. Beside, algorithm software that satisfies the requirements given in section 2 is validated

using TruckMaker. By combining two studies, system becomes implementable to 8x2S truck.

AutoDrop system algorithm has been developed for 8x2S prototype test vehicle and run under PI

INNOVO m250 ECU module using MATLAB/SIMULINK development platform as software.

ECU parameter calibration and embedded program variable monitoring is provided with ATI

VISION based on CCP (CAN Calibration Protocol) as shown in Figure 10.

Figure 10. System Parameter Monitoring with ATI VISION by using CCP

Main principle of algorithm is to decide authorization assignment between ECU and driver about

lift/drop command on retractable axles. Two indicators in cluster (red circles in Figure 10, refer

to Table 2. A2_SIG and A4_SIG) will inform authorization state to driver as an early design.

Vehicle is instrumented by electronic control unit, break-out-box and relay circuit. All I/O s are

connected to ECU trough break-out-box and solenoid valves are driven by relay circuit.

.

Figure 11. Sensor assembly and Electronic Circuit Layout in Cab


6. Results

In this paper an AutoDrop system is introduced and implemented with improved axle load

estimation for compensating arm type suspension by defining correlation between the elements of

compensating arm type suspension which are drive and tag axles. As shown in Figure 9. , fitted

function variation reduced to 489 kg with newly proposed method while in conventional method

this value is up to 2 tons. With the proposed load estimation function, mass estimation error is

found as 450 kg for front axle. For compensating arm type suspension load estimation

performance, to cover worst case, improper 28 loading scenarios has been applied and error is

found as 760 kg near design region which, in fact, is permissible axle load limit.

Figure 12. Measurement Error for Both Front Axle (right) and Drive Axle (left)

Figure 13. Algorithm Test Scenario

An algorithm satisfies the given requirements, is developed and tested under given scenarios. As

0 10 20 30 40 50 60 70 80 900

1

2x 10

4 Front and Rear Axle Group Loads [kg]

0 10 20 30 40 50 60 70 80 900

0.5

1Self Steer Axle position with driver input

0 10 20 30 40 50 60 70 80 900

0.5

1Tag Axle position with driver input

0 10 20 30 40 50 60 70 80 900

50

100Vehicle speed in [kph]

Time [sec]

Vehicle Speed

Driver Input

ECU Output

Driver Input

ECU Output

Front Axle Load

Rear Group Load


it shown in Figure 13 in this scenario, axles are lifted regarding driver demands since the vehicle

is unladed. In 45th

second, tag axle dropping request from driver is neglected because vehicle

speed is over 30 kph. After vehicle is stopped around 60th

seconds, vehicle is started to laded and

the axles are automatically dropped in order.

Conclusions

An algorithm and improved axle load estimation is studied for AutoDrop system for

mechanically suspended trucks. Software is designed using SIMULINK and validated using

TruckMaker before vehicle implementation. The aim is to make the system compatible to

mechanically suspended trucks, thus a load estimation method is proposed for compensating arm

type suspension. Both algorithm and load estimation performance is tested on Ford Cargo 3238S

Truck. Results show that there is an improvement on estimations with the method compared to

conventional measurement techniques and system is implemented on truck successfully.

Acknowledgements

The authors acknowledge the support of the Ministry of Science, Industry and Commerce of

Turkey and the support of Ford Otosan through the SANTEZ Project with code

00905.STZ.2011–1.

References

[1] B.M. Sharma, K. Sitaramanjaneyuiu, P.K. Kanchan. “Effect Of Vehicle Axle Loads On

Pavement Performance” Road transport technology-4. University of Michigan Transportation

Research Institute. Ann Arbor. 1995.

[2] H.M.A. Salem. “Effect of Excess Axle Weights on Pavement Life”. Emirates Journal for

Engineering Research, 13 (1), 21-28 (2008)

[3] Seda Hatipoğlu. “Effect of Maximum Legal Axle Load on Road Life (in Turkish).

[4] O.U. Acar, T. Keleş, Z.Koç, Ş. Güner, M. Duruş, E.Altuğ, L.Güvenç, “Development of

Automatic Lift Axle System for Trucks with Mechanical Suspensions”, IFAC Workshop on

Advances in Control and Automation Theory for Transportation Applications, 2013, Istanbul

implementation of automatic lift axle system for trucks with … · liftable axle mechanism types...

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